Re: [PATCH] bpf: force inc_active()/dec_active() to be inline functions

[Alexei Starovoitov]

On Sun, Jul 23, 2023 at 7:25 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> On Sat, Jul 22, 2023 at 3:48 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> >
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > Splitting these out into separate helper functions means that we
> > actually pass an uninitialized variable into another function call
> > if dec_active() happens to not be inlined, and CONFIG_PREEMPT_RT
> > is disabled:
>
> Do you mean that the compiler can remove the flags automatically when
> dec_active() is inlined, but can't remove it automatically when
> dec_active() is not inlined ?
> If so, why can't we improve the compiler ?

Agree.
Sounds like a compiler bug.

> If we have to change the kernel, what about the change below?

To workaround the compiler bug we can simply init flag=0 to silence
the warn, but even that is silly. Passing flag=0 into irqrestore is buggy.